Process for dewaxing oils



Marh 26, 1940. u. B. BRAY El AL 2,194,968

PROCESS FOR DEWAXING OILS Filed March 31, 1936 2 Sheets-Sheet '1 Waxy022 1 Pro ez zze (igz'ller' 19 Candi"? .580 .5601

Pro azze Siogczge 6' Compressor Z9 Cooler I Zvapordio'r 84 Exchanger INVEN TORS l L Joseph A. Campbe l/J Dewaxed Oil Ulric B.Bra 6: 1:

' ATTORNEY.

Patented Mar. 26, 1940 PROCESS Foa DEWAXING OILS Ulric B. Bray, PalosVerdes Estates, and Joseph A. Campbell, Jr., Manhattan Beach, Calif.,assignors to Union Oil Company of California, Los Angeles, Calif., acorporation of. California Application March 31, 1936', Serial a 71,921.12 Claims. (01. 156-47) The present invention relates to a process fortheseparation of wax from oil. The invention also relates to thefractionation of wax'separated from oils to produce both high and lowmelting point Waxes.- The invention particularly relates to a processfor separating high melting point wax from oil or from a'mixture of lowandhigh melting point waxes by a process corresponding to a leaching outof the oils and soft waxes by 0 means of a suitable solvent fromsolidified discrete particles of oil, soft and 'hard waxes, the discreteparticles being produced by contact of the mixture with the coldleaching solvent at a temperature at which the soft wax and oil issoldble in the solvent but the hard wax is insoluble therein. I I

a It has heretofore been. proposed to separate wax from oils in thepresence of a diluent, preferably a liquefied normally gaseoushydrocarbon, such as liquid propane. In this process, the waxy oi. isdissolved in the liquid propane under superatmospheric pressure and themixture is chilled by reducing the pressure and vaporizing a portion ofthe solvent. By reducingthfe pressure to substantially atmospheric,temperatures as low as -46 F. may be obtained. The chilled mixture isthen filtered, centrifuged or cold settled Waxy. oil is crystallized orsolidified toform a plurality of congealed or solidified particles ofoil and wax. Upon continued contact of the solidilied waxy oilparticles, such as that whichtakes place when these particles settletothe bottom of thecontainer of chilled solvent, solution of the oil inthe resulting solvent takes place leaving Wax matrices undissolved. Thisprocess is commonly referred to as the cold leaching method i'ordewaxing oils. I

In either of the above processes, when operating at a temperature of 40F. which is ap parently necessary in order to produce lubricating oilsof low pour test, the wax cake contains a wide variety of parafiins asregards their melting point. In other wordsjthe wax cake contains notonly the high melting point normal straight chain parafiinsbut also thelower meltf ingpoint paraflins having varying degrees" of 1S0}- paraffincharacteristics. that the low melting point'iso-paraffins must beremoved from, the lubricating oil in order to ob-j tainj an oil ofsatisfactorily low pour point. We. have now found that these low meltingpointisoQ paraifi ns must also be removed from the wax cakes before thelatter can be used" for many,

commercial purposes. 'In other words, it is; not i It has been found nlynecessary to cleoil the wax cakes completely 1'11"!31'18 usual sense ofthe word corresponding to the removal ofjall the lubricating oilfractions which are definitely liquid, at say 30, F., but it is aisonecessary to refractionate the wax ptofi M eliminate iso-parafiincompounds which-hereto-f fore have not been recognized as being presentin the slack waxes to any considerable extent... 20

. In order to accomplish the foregoing, we have found it desirable torework the wax cake produced at' temperatures sufiiciently low toproduce 7 desirable low pour point oils by operating atv f highertemperatures. .In reworking such waxes,

use is made of such solvents at such pressure and temperatureconditions-that not only the oil con' tained in the wax mixture issoluble, but the lower melting point waxes'or iso-parafiins would alsobe soluble to any desired degree. We have found the liquefied normallygaseous hydrocarbons to be particularly useful in this connection.

Suchsolvents include ethane, ethylene, propane,

propylene, butane, butylene, iso-butane and mixtures thereof. The coldleachingmethod aforementioned is particularly adapted for thefractionation of waxes'. With the use of theaforementioned solvents, thevariation of the temperav ture of leaching maybe accomplished bymeans ofvariation of pressure on the volatile solvent.

For example, propane held under a pressure of about 30lbs. per squareinch has a temperature of about 20 F. which is a'suitable temperature gfor theiractionatio'n of some waxes. If desired} a volatile solvent or amixture of volatile'solvents may be employed as the leaching solventwhich has a boiling point at atmospheric pressure of approximately thedesired temperature of leach-.

ing. 1 For example, commercial butane consisting ing solvent. atatmospheric pressure.

We have also discovered that the mixture of" waxes containingconsiderable amountsof lubricating oil, such as a waxy lubricating oildistillate or a slack wax which has been separated from oil, may befractionated by means of solvents into a high melting point wax, a lowmelting point wax and a lubricating oil of low pour point in a simple,economical and efficient manner. Thus, instead of separating a mixtureof low and high melting point wax from the original oil containing thesame at a low temperature of say 4G F. and then fractionating theseparated waxes into high and low melting point waxes, we have found itpossible to subject the original stock to cold leaching in a suitablesolvent in accordance with the method hereinafter described at atemperature at which the oil and soft waxes or iso-paraffins which aresoluble in the leaching solvent but in which the high melting pointwaxes are insoluble. In this process, a separation is made of the highmelting point waxes on one hand and the soft wax and lubricating oildissolved in the solvent on the other hand. The solvent solution of thelow melting waxes and oil separated from the high melting point waxes ata temperature in which such waxes are insoluble is then furtherchilledto precipitate the soft waxes which may be separated from thesolution of oil and solvent by any convenient method such as byfiltration, settling or centrifuging. When this process is employed, agreater advantage is obtained not only in the improvement obtained inthe operation of the process with regard to filter rates and filteroperation but that a large percentage of the cost of chilling iseliminated. Thus, when a liquefied normally gaseous hydrocarbon isemployed as the diluent-refrigerant for separating the mixture of waxesfrom the oil to produce a lower pour point oil and for treating theseparated mixture of waxes in order to remove the high melting pointwax, the cost of reliquefying the gaseous auxiliary equipment and alsonecessitates provision of large storage capacity for thediluentrefrigerant.

Thus, in the operation of the process forming the subject of ourinvention, it will not be necessary to subject the separated mixture ofhigh and low melting point wax to fractionation in a solvent. It ismerely necessary to subject the original stock to a leaching operationat a controlled temperature to separate the high melting point waxes andthen further chill the solution containing the soft waxes by evaporatinga portion of the solvent under reduced pressure to obtain a lowertemperature sufiicient to precipitate the softer waxes. This combinationof the cold leaching process followed by precipitation of the remainingwax avoids duplication of auxiliary equipment and also the refrigerationrequired for the dewaxing operation is advantageously employed for theoperation of the wax-leaching unit making it unnecessary to provideduplicate refrigeration equipment. However, it will be understood thatthe fractionation by leaching of the mixture of high and low meltingpoint waxes which have been separated from oils at temperaturessufficient to separate both types of waxes as a mixture is also withinthe scope of our invention.

It is therefore an object of our invention to fractionate a mixture ofhigh and low melting point waxes into a low melting point wax and a highmelting point wax. It is a further object of our invention to accomplishthe fractionation by a leaching process in a suitable solvent,particularly a liquefied normally gaseous hydrocarbon which ismaintained at a suitable temperature so that the fractionation of thewaxes may be accomplished.

It is a further object of our invention to introduce a wax-oil mixtureinto a cold leaching solvent maintained at a temperature so that thesoft wax and 'oil are dissolved in the solvent while the hard or highmelting point wax remains insoluble in the cold solvent, in separatingthe solution of soft wax, oil and solvent from the hard wax, in chillingthe last mentioned solution to a low temperature sufficient toprecipitate the soft wax, in separating the precipitated soft wax fromthe solution of oil and solvent and in separating the solvent from theoil.

Other objects and advantages of our invention will be apparent from thefollowing description of the invention taken from the drawings which arenot to be considered as limiting the invention.

In the foregoing description of the preferred embodiment, the use ofcommercial propane as a combined diluent and refrigerant has beendescribed. However, it should be understood that other liquefiednormally gaseous hydrocarbon such as ethane, ethylene, propane,propylene, butane, isobutane, butylene, etc. may be used separately orin admixture with each other. Instead of using liquefied normallygaseous hydrocarbons other normally gaseous diluent-refrigerants may beemployed such as methylether, methyl chloride, dichlor-difluor-methane.Also admixtures of the foregoing normally gaseous diluent refrigerantsand normally liquid hydrocarbons, such as gasoline, casinghead gasoline,naphtha, normally 1 liquid anti-solvents for wax such as acetone, acid.esters, mixtures of benzine with naphtha, mixtures of acetone andbenzol, and the like, may be employed. If desired, the normally liquidhydrocarbons such as pentane and hexane may be employed as the leachingsolvent. These may be chilled by external means as is well known bythose skilled in the art. In the preferred embodiment practicallycomplete separation of the wax from the oil is effected by the use ofcommercial propane as the diluent refrigerant.

In the drawings, Fig. 1 represents a schematic flow diagram of a processin which the waxy oil is first subjected to leaching in order toseparate the hard wax and then the solution of oil,

soft Wax and diluent is further chilled and filtered to separate thesoft wax. Fig. 2 represents a flow diagram of a process in which amixture of soft and hard wax is separated from the waxy oil and then themixture of waxes is subjected to leaching in order to fractionate thewax into soft and hard wax.

Referring to Fig. 1, a waxy stock such as an S. A. E, 20 distillateproduced by the vacuum distillation of a Santa Fe Springs crude is drawnfrom tank 1 via line 2 and pumped by pump 3 through line 2a controlledby valve 3a through spray head 4a into the first leaching column orextractor A. The leaching column is first filled with a cold leachingsolvent, for example liquid propane at an appropriate temperaturesufficient to dissolve the oil and low melting point isoparaffin typewaxes which may be at a temperature of approximately 10 F. to 40 F.which represents the temperature in which the oil and soft waxes aresoluble in the cold leaching solvent but only small amounts of theharder or high melting point wax are soluble in the solvent.

Filling of the leaching column is accomplished by withdrawing liquidpropane from propane storage tank under superatmospheric pressure atabout normal temperatures and passing it via.

line 6 controlled by valve 1 by means of pump 8 into propane chiller 9where a portion of the via line l6. By reducing the pressure in chiller9 to approximately 20 to 65 lbs. per square inch,

. the temperatureof the remaining propane will be lowered toapproximately 10 F. to 40 F. The chilled propane is withdrawn from thebottom of chiller 9 via line i! controlled by valve 18 and is passed bypump l9 into the first leaching column A via lines 2!), 20a controlledbyvalve Zia and line 22a controlled by valve 23a.

When the required amount of propane has'been introduced into theleaching column A, thewaxy oil at an appropriate temperature is sprayedinto the vessel. The temperature at which the waxy oil is heated priorto spraying it into. the cold leaching solvent will depend upon whetherit is desirable to solidify the sprayed waxy particles in the form ofcornfiake-like shapes or as pellets, discs or strings when the waxy oilis contacted with the cold leaching solvent. We have found it desirableto effect the solidification of the sprayed waxy oil droplets ascornflake-like shapes since it requires less time for the leachingsolvent to leach the oil from the solidified wax structures although thesolidification as pellets, 'discs or strings is within the scope of ourinvention. The solidification of the waxy oil in the cold leachingsolvent as cornflake-like shapes may be accomplished by first heatingthe waxy oil so that it assumes the viscosity of 350 seconds SayboltUniversal and then spraying the waxy oil through a spray head providedwith a large number of small nozzles. The introduction of the waxy oilinto the cold leaching solvent at a viscosity above 350 seconds SayboltUniversal results in the solidification of the Waxy stock upon contactwith the solvent as pellets, discs or strings. For the S. A. E. 20 waxydistillate obtained from the Santa Fe Springs crude oil, it has beenfound that the desirable temperature of heating prior to the spraying isabout 110 F. or 120 F. For an S. A. E. 50 stock the temperature shouldbe about 150 F. This temperature, of course, will vary with other waxystocks. Also, the temperature of heating will depend somewhat upon thesize of the nozzles employed in the spray head as will be readilyunderstood by those skilled in the art.

We have obtained good results when using liquid propane as the leachingsolvent with as low as three volumes of the propane to one of the waxyoil in the initial leaching column A. However, by employing largeramounts of pro pane, say 10 volumes of the propane to one of the oil,the leaching of the oil from the solidified particles of oil and waxwill take place more rapidly and also less foaming will be encounteredduring the addition of the last part of the waxy oil. However, it is noteconomically desirable to employ more than 10 volumes of propane due bymaintaining pressure therein.

to the large capacity of the leaching columns required to effect theleaching operation and the cost of the chilling and due also to the costof chilling and recovering additional solvent.

'' It will be observed that when employing a liquefied normally gaseoushydrocarbon, such as liquid propane, as the leaching solvent, a portionof the solvent will vaporize immediately upon contact with therelatively warm waxy oil thus creating a turbulent condition in thecolumn. This is not. desirable since the leached wax matrices beingfragile are readily disrupted by any sub stantial agitation into finelydispersed wax particles which are difiicult toseparatefrom the oilsolvent solution. t is therefore preferable to maintain quiescentleaching conditions and to prevent substantial boiling in the leachingcolumn. This may be accomplished by controlling the vaporization of thesolvent in the columns or The pressure may be controlled by means ofvalves 85a, 85b, 85c, 8512, on lines 86a, 86b, 86c, 86d, respectively,of

leaching columnsA, B, C, D, respectively. If desired, an extraneous gas,such as air, carbon dioxide or other non-miscible gases may beintroduced into the columns to create a pressure therein and suppressboiling. Also, in the case where a liquefied normally gaseoushydrocarbon is employed as a leaching solvent which has a vapor pressuregreater than atmospheric at the leaching temperatures, valves 85a, 85b,85c, 85d, on lines 86a, 86b, 86c, 85d, respectively, are employed formaintaining the pressure in the columns so that the desired temperaturemay be maintained in the leaching columns. It is also desirable toprevent infiltration of heat from the outer walls of the leachingcolumns sincethis causes propane to boil therein. One method forpreventing this, is to jacket the outer walls of the columns and tocirculate a cold mediumthrough the jacket.

The waxy stock'is allowed to remain in contact with the leaching solventfor a period of time, say minutes to 2 hours, to allovva substantialquantity of the oil occluded in the Wax matrices to be leached by thesolvent. At the end of the leaching period, the fresh propane isintroduced at the top of the vessel from propane chiller 9 and valve 23bis opened and the solution is drawn off from the first leaching column Aand is transferred by pump 58a through lines 24a, 25a and 22b into thesecond leaching column B. The introduction ofsolution of oil and solventinto the second leaching column B is continued until substantially allof the solution in column A is displaced with fresh propane whereuponwaxy oil from tank I is sprayed by line 2?) controlled by valve 3bthrough spray head 41), the introduction of waxy oil being continueduntil the required amount of oil has been introduced into the column B.In the meantime, the wax structures in column A are subjected toleaching with fresh solvent which lowers the oil content of the waxstructures. When sufiicient leaching time has been allowed in column B,the oil propane solution is transferred via the bottom of the leachingcolumn B by pump 58h through lines 24b, 25b and 220 controlled by valve230 into the final leaching column C. Simultaneously therewith,the'relatively more diluted propane oil solution from leaching column Ais transferred to leaching col.- umn B and fresh propane is introducedinto leaching column A. l

Waxy oil is then introduced into the column C head and the introductionof the waxy oil is continued until the desired amount of oil has beensolidified in column C.

The displacement of propane oil solution in leaching column A isrepeated a number of times, depending upon the total number of stages orextraction vessels in the system, say three as shown in the drawings,until substantially oil-free propane is withdrawn from the bottom of theleaching column. The oil propane solution is then withdrawn from thebottom of the last leaching stage C via pump 58c and lines 24c and filocontrolled by valve 280 and is passed through line 29 to either of thealternate chillers 3i and 33 via either line 38 controlled by valve 33aor line 32 controlled by valve 32a. The solution in chillers 3i and 33is further chilled to a temperature sufficiently low to precipitatesubstantially all of the remaining wax contained therein, preferably bygradually reducing the pressure to substantially atmospheric byoperation of valves 34a and Shot on lines 34 and 35 respectively. Thiscauses propane to be vaporized which chills the remaining solution tothe desired dewaxing temperature, the propane vapors being withdrawn vialine 3 3 or 35 depending upon which of the chillers are in operation.The vapors then pass into line 36, are compressed by compressor 3'3 andare returned to propane storage tank 5 via line 38, cooler l5 and lineIt. Chilling is preferably accomplished at a rate not in .excess ofsubstantially 3 F. per minute.

The chilled oil, propane and wax slurry is withdrawn from the bottom ofthe chillers 3| and 33 via lines 39 and All respectively, which arecontrolled by valves 39a and 46a respectively, the mixture then passinginto line i! is pumped by pump 42 through line 43 to filter 44 where thewax precipitated from solution by chilling is separated from the oil andsolvent. The clear solution is then passed through line 45 through heatexchanger 16 where the temperature of the clear solution is raised to atemperature sufficient to vaporize the propane, after which thepreheated solution is passed through line 41 into evaporator 48. Thepropane is vaporized from the oil in evaporator til, aided by steamcirculated through closed coil 55}, the vapors passing through mistextractor 5;; and are withdrawn via line 5| controlled by valve 5m andare sent to propane storage tank 5 via cooler 52, lines 53 and 50,compressor l2 and condenser 15. The dewaxed oil is withdrawn from thebottom of the evaporator via line and is pumped by pump 55 through valve5 into dewaxed oil storage tank 51.

The separated wax in filter M is withdrawn via line 73 controlled byvalve 13a and is passed through heat exchanger Hi and line l5 intoevaporator lS provided with closed heating coil l! and mist extractor'18 in which the wax is depropanized. The clepropanized low meltingpoint wax is withdrawn from evaporator 16 via line 88 and is pumped bypump 8| through valve 82 into storage tank 83. Propane vaporized inevaporator i=3 is withdrawn via line l9 controlled by valve 79a andpasses via line 84 into line 5!.

As stated above, when substantially all of the oil and soft wax oriso-paraffins have been leached from the wax matrices with fresh propanein the first leaching column, the latter is cut out of the system andthe fresh propane is introduced into leaching column B which thenbecomes the first leaching column in the system. Leaching column D isthen cut into the system by filling the vessel with propane oil solutionwithdrawn from leaching column C via lines 240, 25c and 22d controlledby valve 23d. This, of course,.is accomplished until the solution incolumn B has been displaced with fresh liquid propane. Waxy oil is thensprayed into column D via lines 2 and 2d controlled by valve 3d andspray headld. As in the case of column A, when the leaching operation incolumn B is substantially completed, the propane oil solution in columnD is passed to the chillers via lines 2M, Zld controlled by valve 28d,line 29 and either line 30 or 32. The propane solution from column B isthen transferred to column C and thence to column D, fresh propane beingintroduced into column C via line 28c controlled by valve 210 and line220 controlled by valve 230. Column C then becomes the first leachingcolumn, column B the second leaching column and column A after removingthe wax therefrom becomes the third leaching column.

We have thus described a process for separating wax from oil involvingleaching of the wax structures wherein a plurality of leaching columnsare provided so interconnected that the flow from one leaching columnmay be diverted from one to the other and the leaching columns are sointerconnected that they may be rotated in such manner that asemi-continuous operation may be carried out with the use of an extraleaching column. Also, in the above description, discontinuous batchleaching is shown. However, the invention is not to be considered aslimiting thereto since it embraces continuous flow of leaching solventfrom one column to another, that is, the operation may be carried out insuch manner that fresh propane is continuously introduced into the firstleaching column and concentrated propane oil solution containingiso-paraffins or soft wax is withdrawn from the last leaching stage andpassed to the chillers. Thus, we may operate in such manner that the oilsolvent solution and soft wax may be continuously passed to thechillers. The production of the oil propane solution from the lastleaching column is controlledby time, for example, if approximately onehour is calculated from the rate of flow of wash propane in the systemto be required for displacing the propane oil solution in any of theleaching columns, then the first hours withdrawal of propane solutionfrom the vessel just charged with oil is sent to the chillers. Thepropane solution withdrawn subsequently is then used as Wash propane inthe second leaching column. If in charging an empty leaching column fora new cycle, all of the propane solution required for leaching andwashing the waxy stock for the first time is accumulated in the leachingcolumn before introducing the waxy stock, it is desirable, although notnecessary, to interrupt the flow of wash propane while the waxy stock isbeing introduced, giving periodical interruptions in the flow of bothwash propane and propane oil solution. To avoid interruption in the flowof wash propane, the introduction of waxy stock into the fresh or emptyleaching column may be begun after only a part of the propane solutionrequired for filling the leaching column is introduced and the rate ofaddition of waxy stock be adjusted so that the addition of waxy stock iscompleted by the time the liquid reaches the proper level.

In order to minimize the amount of entrained wax particles in thesolution withdrawn from the bottom of the leaching vessels, filter beds5%, 59b, 59c, 5911, are provided at the bottom of the I ferred forwashing and filtering the wax taken leaching vessels to hold theleaching waxstructures in the column while the propane solution isallowed to wash through it. For this purpose, any desirable materialmaybe provided, such as pads of steel wool, broken glass, stones, pebbles,

and/or canvas filter.

After the washing of the wax structures in any extractor is consideredcomplete and the extractor is cut out of the system, the wax structuresare then removed from the leaching column and are distilled to recoverthe wax and solvent. The removal of the wax structures may be 8,0601..-plished by introducing a warm liquid into the leaching columns via lines60a, 60b, 80c and Bild to partially or totally melt the wax structures,the

melted wax being withdrawn from the bottom of the leaching columns bypumps 580., 58b, 58c, and 58d, and valves Gla, 5 I b, Bio, and Bldrespectively, and passed into line 62 controlled by valve 62a to heater63 where the structures are heated to a suificient temperature tovaporize the propane after which the mass is passed through lines 64into evaporator 65 where the propane is vaporized from'the wax aided bysteam circulating through closed coil 66, the vaporized propane passingthrough mist extractor 67 into line 68 controlled by valve 68a. The highmelting point Wax withdrawn from the bottom of the evaporator 69 ispumped by pump through valve H into high melting point wax storage tank12. This waxmay be further treated such as with sulfuric acid and alkaliand/or clay to produce a high melting point water white wax suitable Ifor the production of candles and the like.

i In another method for removing the wax from the leaching column thewax structures may be partially disintegrated by mechanical agitationsuch as by means of scrapers or stirrers built into the leaching columnsor by blowing the structures with propane or other gas. The mass may betransferred from the bottom of the leaching column by means of a screwconveyor or transferred as a slurry by pressure, the slurry beingproduced if desired, by mixing the wax with propane to form a pumpable'mass. This mass may be filtered, centrifuged or settled to concentratethe wax particles and recover chilled propane suitable for washing otherwax structures. The concentrated wax or wax cake may be washed withfurther quantities of fresh propane to reduce the oil content stillfurther. The use of a continuous oil drum type filter is preout of theleaching columns. The wash propane may be employed for washing other waxstructures in keeping with the spirit of the invention.-

When employing filter beds in the extraction columns, the wax structuresmaybe removed by first withdrawing as much of the liquid propane aspossible through the filter bed without however bringing the liquidlevel below the top edge of the filter bed. The filter is thenback blownwith propane gas and additional wash propane is introduced at the bottomof the filter bed. The back blowing washes wax out of the filter bedinto the wax slurry on the top. The back blowing can be very violent, ifdesired, in fact so violent that the, entire filter bed is blown up intosuspension along with the wax in the propane liquid which will have nowbeen brought to a convenient height inthe extraction vessel. Uponstopping the violent agitation by blowing the heavy filter bed materialwill settle with extreme rapid- Y ity leaving practically all. of thewax suspended as a slurry in the propane phase which can then bedecanted off at a point just above the top, of the filter bed. In thismanner the filter is then cleaned and ready for another cycle. Inbeginning a fresh cycle the first production may be recycled if cloudy.I

The foregoing invention has been described as used for the separation ofwax from an S. A. E. 20 lubricating oil distillate produced from SantaFe Springs crude petroleum. It should be under-' stood, however, thatthe invention is equally applicable for the separation of wax from anywaxbearing oil whether ,it consists of a lubricating In some instances,we find it desirable to introduce the wax-oil mixture into the coldleaching solvent as a finely divided solid. The wax-oil mixture may besolidified by lowering its. temperature to produce a solid mass whichcan then be mechanically broken up by any suitable means into ribbons,strings, or irregular shaped particles which could then be mechanicallyintroduced into the cold solvent. It is desirable to break the mass intosuch particles that the solvent need not penetrate over 4 th inchsections and pref-1 erably not over j gth inch sections as sectionsthicker than this do not leach within a reasonable length of time.

There are several methods which are applicable for solidification andbreak-up of the oil-wax mixture. One method involves the solidificationof the oil and Wax mixture in blocks or rods which is then broken up byslicing ofi thin wafers by means of warmed knives, similar to a butchersslicing machine.

In another method, the wax-oil mixture is maintained in a trough in afluid condition by heating, if necessary. A chilled cylinder is allowedto dip into the liquid which is rotated at such a speed that a film ofsolidified wax-oil mixture of the desired thickness of %;th to 95th inchis deposited on the cylinder. This film may then be removed by a scraperto produce flakes of the solidified material which can then be fed intothe cold leaching solvent.

In another method, the oil-wax mixture is chilled to a temperature belowthe ordinary solidification point but still the temperature issufficiently high that the mixture can be mechanically worked or kneadedinto a plastic condition. This plastic material is then extruded throughsmall orifices of /;,th inch or less in diameter and preferably aboutAlths inch. The extruded material is then allowed to fall into the coldsolvent to be solidified'as strings or worms. However, in this method,the pumping of the plastic material any distance presents obvious thedegree of chilling controlled to obtairr'thedesired plastic condition.Mechanical devices for chilling the wax-oil mixture-below itssolidification point and at the same time keeping the,

chilled material plastic by mechanical working are well known to thoseskilled in the art, and therefore need not be .fully described herein.

I Theintroduction of the wax-oil mixture as a 7 free-falling stream at asufficiently high temperature that it is liquid, has been describedabove. However, in some instances it is desirable to adjust thetemperature of the wax-oil mixture prior to its introduction as near thesolidification point of the particular oil-wax mixture as possible.

If desired, the liquefied oil-wax mixture and solvent may be introducedsimultaneously as impinging sprays in the vapor spaces of the leachingvessel and then allowed to fall together into the liquid in the vessel.The solvent may be introduced either in a pre-cooled condition or when aliquefied normally gaseous hydrocarbon is employed, it may be introducedunder pressure and allowed to expand in direct contact with the oilwaxmixture. In the latter case, the expansion of the liquefied normallygaseous hydrocarbon results in a vaporization of a portion of thesolvent and thus chills the remainder of the solvent and also theoil-wax mixture. The length of fall is preferably sufficient so that theoil-wax mixture is solid when it finally comes to rest in the vessel.When using a liquefied normally gaseous hydrocarbon as the leachingsolvent, solidification takes place so rapidly as to be practicallyinstantaneous. The oil-Wax mixture should be sprayed through smallorifices so that the resultant solidified particles present sections -thto %th inch. This method of operation has the advantages of a saving incharging time when used in the countercurrent downfiow leaching.

There is a tendency when employing certain solvents for the solidifiedoil-wax mixture to float on the solvent for such a length of time thatthere is a serious loss of time efiiciency in charging the wax-oilmixture to the leaching vessel. This difficulty may be overcome bygentle mechanical agitation of the solidified particles in the leachingvessels such as by means of stirrers or a portion of the solvent orsolvent and oil from the bottom of the leaching vessel may berecirculated so that a stream of the liquid. is continually sprayed overthe surface of the oil-wax mixture in the leaching vessel. This willenable the solidified wax-oil particles to settle to the bottom of thevessel.

In some cases it is desirable to introduce other materials into theoil-wax mixture for the purpose of strengthening the solidifiedparticles. We have found this to be particularly desirable in oil-waxmixtures of low wax content. We have found that when the wax structureafter the removal of the oil or oil and soft waxes represents less than12% to 15% by volume of the original wax-oil mixture, it is very thinand tenuous and is easily crushed by the weight of the wax above it, orit is broken up by boiling or by eddy currents of the solvent. Whenbroken up, the wax structure settles and becomes compacted into animpervious mass which retards or prevents further leaching. We havefound that the addition of other materials to the wax-oil mixture beforesolidification will prevent this occurrence. For this purpose We may usematerials which have heretofore been used to improve filtrationcharacteristics of the chilled mixtures containing'precipitated wax.Such materials include asphalt, cracked petroleum residues, oxidized waxand the like. In some instances we find it desirable to increase the waxcontent of the particular wax fraction desired to be removed by leachingso that the wax content represents at least 12% to 15% by volume of thewaxoil mixture introduced intothe leaching vessel. If desired,emulsified water in the oil-wax mixture may be used for strengtheningthe wax structures. If desired, the laying down ofalternate layers ofsolidified oil-wax mixture and ice, asphalt or sand or the randommixture of the solid particles of ice, asphalt or sand in the solidifiedoil-wax mixture in the solvent may be employed.

The separation of the added asphalt and the like from the wax afterleaching may be accomplished by breaking up the leached structures afterthe desired degrees of leaching has been accomplished. This may be doneeither in the leaching vessel or in a separate container but preferablyin the latter. The mixture may be heated to a temperature which issuificiently high to dissolve all the wax and allowing the mixture tosettle. The asphaltic materials or oxidized wax and the like presentwill then separate out either in a liquid or solid phase and areseparated from the wax by decantation or filtration. If desired, the waxslurry as removed from the bottom of the extraction vessels may beheated without first removal of solvent and the heated mixture thenpassed to a quiescent zone under pressure where the asphaltic bodieswill settle out.

To illustrate the advantages obtainable by carrying out the process ofextracting wax from oils forming the subject of our invention, thefollowing is submitted which, however, is not to be considered aslimiting our invention.

An S. A. E. 20 waxy distillate obtained from a Santa Fe Springs crudeoil is first enriched with about 8% by volume of hard wax previouslyobtained from the same stock and is then heated to a temperature ofabout 110 F. or about 20 F. above its pourpoint so that the waxy oil hasa viscosity of about 350 seconds Saybolt Universal. The pro-heated waxyoil is then sprayed into three leaching stages in accordance with theforegoing disclosure. Propane at about 20 F. and maintained underpressure of about 30 lbs. per square inch is employed as the leachingsolvent. The initial ratio of propane to oil employed in the first stageof leaching was approximately 5 volumes of propane to one of the waxyoil, and the total amount of propane passing through the leaching vesselfor complete extraction of the charge Was 15 volumes based on originalcharge of Waxy oil. The propane oil solution withdrawn from the bottomof the first stage was employed as leaching solvent in the second stageand that withdrawn from the bottom of the second stage was employed inthe third stage. In the subsequent leachingstages the pressure andtemperature conditions were maintained substantially the same as thatmaintained in the first leaching stage. The propane-oil solution fromthe third stage of leaching, corresponding to the third use of thepropane, at a temperature of about 20- F. was further chilled byevaporative refrigeration, that is, by vaporizing propane from thechilled mixture at a rate not substantially greater than 3 F. per minuteuntil a temperature of -40 F. was attained in thechiller. The chilledmixture was then filtered to remove the soft wax which precipitated uponchilling. Upon completion of the run approximately i of dewaxed oil wasproduced having a pour point of -5 F. The high melting pointwax wasrecovered from the leaching columns, after depropanization, had amelting point of 145 .F. and represented approximately 16% of theenriched waxy oil. Approximately 17% of the soft wax was recovered byfurther chilling the propaneoil solution from the leaching column andhad a melting point of F.

As another example, an S. A. E. 20 waxy distillate in which 0.5% byweight of oxidized wax had been dissolved was commingled with 250 volumepercent of liquid propane at a temperature atmospheric until atemperature of about 40" F. was obtained in the chiller. Duringchilling, make-up propane was added to the charge in order to maintainthe ratio of 2.5 volumes of propane to one of the waxy stock. Thechilled mixture was then filtered to separate the wax and addedfiltration aid, 1. e. the oxidized wax from the solution of propane andlow pour point dewaxed'oil. The wax cake was then depropanized bydistillation to produce a slack wax of about 126 F. melting point.

The slack wax was then purified in accordance with the manner describedas follows: It was heated to a temperature of about 145-F. and thenextruded through small orifices of about in diameter and allowed to fallinto a body of cold solvent consisting of a mixture of normal andiso-butane maintained at atmospheric pressure and at a temperature ofabout 20 F. The

melted wax was solidified upon contact with the cold butane intoworm-like particles. After leaching the wax structures with liquidbutane at 20 F. in three stages as aforesaid, employing approximately 15volumes of the liquid butane, the leached wax structures were dischargedfrom the leaching vessel in the form of a slurry, a portion of thebutane being removed along with the wax structures to form the slurry.

The slurry was then heated without distilling off the butane to atemperature of about 200 F. under a pressure of about 220 lbs. per sq.in. and was then passed to a settling chamber where it was allowed toremain quiescent for a period of time. During this quiescent period,settling of the filtration aid took place so that a practically clearbutane-wax solution free from suspended solid material was decanted fromthe settling vessel. The bottoms in the settling vessel consistedlargely of the filtration aid. The latter was separated from thesolution of butane and wax and after heating to remove contained butane,was recycled for admixture with waxy stock to be dewaxed.

The warm solution of butane and wax was decanted and filtered to removelast traces of entrained solid particles and was then distilled toseparate the butane from the wax to produce a high melting point wax.This wax was then treated at a temperature of about 175 F. with about25lbs. of H2SO4 per barrel of the melted wax. The acid-treated wax wasthen treated with an adsorbent clay in the proportion of 10% by weightat a temperature of about 350 F. and was then filtered. The thus treatedwax had a melting point of 146 R, an NPA color of 1.5 when melted and anoil content of less than 4%. In some cases we find it desirable to acidand clay treat the wax in a solution of a solvent such as butane, at anelevated temperature. In most cases it is not necessary to treat theacid treated wax or wax solvent solution with alkali when clay treatmentis employed although this may be employed.

The solution of butane, oil and soft wax sepa- 20 waxy distillate inorder .to recover as much of the oil as possible or it may be subjectedto releaching by spraying it" at a temperature of about ,F. in body ofliquid propane maintained ataa temperature of about 40 F. in which casea low pour point oil may lee-separated from the chilled structures toproduce a low melting point wax.

In the foregoing example, we have described a process wherein a mixtureof low and high melting point waxes containing some oil is separatedfrom a waxy distillate by the solution and precipitation methodemploying liquid propane as a diluent-refrigerant. The high meltingpoint wax was recovered from the separated waxes by a leaching, processin liquid butane. Instead ofseparating the mixture of waxes by thesolution and precipitation method, we find it desirable to separate themixture by leaching in liquid propane at a temperature of 40? F. andthen fractionate the mixture of waxes into, a high melting point wax andfoots oil by introducing into the vessel containing the mixture ofWaxes, liquid propane under a pressure sufiicient to provide atemperature of about 20 F. in order to allow the latter to dissolve thefoots oil from'the solidified wax structures, and thus produce the highmelting point wax. The solution of foots oil in the liquid propane at atemperature of 20 F. may then be chilled by evaporative refrigeration,i. e., by reducing the pressure to atmospheric so as to-chill thesolution to .40 F. and thus precipitate the soft wax which may beseparated from the mixture by melting, filtering or centrifuging.

The foregoing description of our invention is not to be taken aslimiting since many variations may be made within the scope of thefollowing claims by those skilled in the art without departing from thespirit thereof.

We claim:

1. A process for separating wax from a waxoil mixture which compriseschilling a waxy oil to a sufficiently low temperature to precipitate amixture of soft and hard waxes, separating said mixture of soft and hardwaxes from the oil to produce alow pour point oil, introducing saidmixture of soft and hard waxes into a cold solvent capable of dissolvingthe soft wax but incapable of dissolving the hard wax at the temperatureemployed, solidifying said mixture of waxes by contact with said solventand allowing said'solidified mixture of waxes to remain in contact withsaid solvent for a sufficient period of time to permit said solvent todissolve the soft wax, separating the solution of soft wax from the hardwax.

2. A-process as in claim 1 in which the solvent employed comprisesliquid butane.

3. A process for separating wax from a waxoil mixture which comprisesmixing a waxy oil with a small quantity of a filter aid, chilling themixture of a waxy oil and filter aid to a temperature sufficiently lowto precipitate a mixture of hard and soft waxes containing said filteraid, separating the precipitated hard and soft waxes and filter aid fromthe oil, heating said separated mixture to melt the'same, introducingsaid mixture into a relatively large body of a cold solvent maintainedat a temperature sufficient to dissolve oil and soft wax contained insaid mixture but not substantial quantities of the hard wax, solidifyingsaid mixture of waxes by contact with. said solvent and allowing saidmixture to remain in contact with said solvent for a sufficient periodof time to permit said solvent to dissolve the soft wax and containedoil, separating the solution of soft Wax from the hard wax containingfilter aid, mixing the hard wax and filter aid with a diluent andheating said mixture to melt the wax, and separating the filter aid fromthe solution of hard wax and diluent. i. A process for separating waxfrom a mixture containing relatively hard wax, relatively soft wax andoil which comprises first separating a mixture of the relatively hardwax and the relatively soft wax from the oil, remelting said mixture ofhard and soft waxes, introducing said mixture of relatively soft andhard waxes in the substantial absence of a diluent into a solventcapable of dissolving the soft wax but incapable of dissolving the hardwax at the temperature employed, solidifying said mixture of waxes bycontact with said solvent and allowing said solidified mixture of waxesto remain in contact with said solvent for a sufiicient period of timeto permit said solvent to dissolve the soft wax but not appreciablequantities of hard wax and separating the solution of soft wax from thehard wax.

5. A process according to claim 4 in which the solvent employed isnormally gaseous.

6. A process as in claim 4 in which the solvent employed is normallyliquid.

I. A process for separating wax from a waxoil mixture which comprisescommingling said wax-oil mixture with a diluent, chilling the mixture toa sufficiently low temperature to precipitate a mixture of soft and hardwaxes, separating said mixture of soft and hard waxes from the oil anddiluent, heating said mixture of soft tained at a temperature sufficientto dissolve oil and soft wax but not substantial quantities of hard waxcontained in said congealed mixture, extracting the oil and soft waxcontained in said congealed wax mixture by means of said solvent toleave a matrix of relatively hard wax substantially free from relativelysoft wax and oil and separating the solution of soft wax from thesolidified hard wax.

8. A process as in claim 7 in which the solvent employed to dissolve thesoft wax content from the mixture of soft and hard waxes is normallygaseous.

9. A process as in claim 7 in which the solvent employed to dissolve thesoft wax content from the mixture of soft and hard waxes is normallyliquid.

10. A process as in claim '7 in which the solvent employed to dissolvethe soft wax content from the mixture of soft and hard waxes is normallyliquid and has chemical properties similar to acetone.

11. A process according to claim 7 in which the soft wax separated fromthe hard wax is subsequently mixed with the wax-oil mixture to bedewaxed.

12. A process according to claim 7 in which the solvent employed todissolve the soft wax content is different from the diluent employed toseparate the mixture of soft and hard waxes from the oil.

ULRIC B. BRAY. JOSEPH A. CAMPBELL, JR,

